After a practice battle, you are brought before the king of Nohr.
Normal and Hard Difficulty
When you first start the battle, walk onto the Dragon Vein and choose Dragon Vein to clear the debris. Only Corrin can do this.
The healing area is a 3x3 square. As long as your units stand on these tiles, they will regain HP on each turn.
You can put your three units in the middle of this square, with one unit blocking the left entrance, one blocking the right, and the other in the center. The center unit will assist in the attacks that the left and right units do.
Put Corrin in the center so Gunter and Jakob/Felicia can weaken the attacks and Corrin can finish them off, getting plenty of EXP for the kills. Jakob/Felicia can go on the left and Gunter can go on the right.
Focus on defeating Rinkah and Kaze first, then kill the remaining enemy units.
In Lunatic mode, you will need to protect Jakob/Felicia from taking too much damage. Focus on getting rid of Kaze and Rinkah as soon as possible. But be sure to make Jakob/Felicia gain some levels during this chapter so that he/she can provide enough support in the next one.